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doc: update timestamp validity for latency measurement

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Updated the doc on how packets are marked to identify
their timestamp as valid and considered for latency
measurement.

Suggested-by: Bao-Long Tran <longtb5@viettel.com.vn>
Signed-off-by: Reshma Pattan <reshma.pattan@intel.com>
This commit is contained in:
Reshma Pattan 2018-10-04 13:23:59 +01:00 committed by Thomas Monjalon
parent eaee965903
commit 999aa0635c
1 changed files with 9 additions and 0 deletions
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doc/guides/prog_guide/metrics_lib.rst
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@ -271,3 +271,12 @@ de-initialise the latency library.
.. code-block:: c
rte_latencystats_uninit();
Timestamp and latency calculation
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The Latency stats library marks the time in the timestamp field of the
mbuf for the ingress packets and sets the ``PKT_RX_TIMESTAMP`` flag of
``ol_flags`` for the mbuf to indicate the marked time as a valid one.
At the egress, the mbufs with the flag set are considered having valid
timestamp and are used for the latency calculation.